the boiler by avoiding unequal expansion due to cold feed, and
also promote circulation. Injectors belong to this class.
The Superheater^ as a boiler apparatus, has already been
P. 696. Fuel. — The calorific value of a given fuel can
be obtained as on p. 697, or may be expressed as a simple
formula, where the weights of other elements are given in terms
of the carbon. Thus (p. 697, lines 7 and 8) i Ib. of H produces
4-28 times the heat i Ib. of C does; and again (p. 697, line 20)
i Ib. of H must be deducted for every \ Ib. of O present.
Calorific value ir
B.T.U. per Ib.
14500 (C +4-28 (H-
where C, H, and O are the actual weights of 'these elements per
Ib. of fuel. Now as 966 B.T.U. evaporate i Ib. of water from
and at 212°,
Ibs. of water evaporated per Ib. fuel =
given in what are called evaporation units. For the sample on
p. 697 this would be 15*3 Ibs. of water.
A directly practical test is, however, always advisable, and for
this we may refer to Thompson's fuel calorimeter, Fig. 868. A
fuel chamber A is placed on a stand, immersed in a vessel of